1. Technical Field
The present invention relates to wireless communication in general, and in particular to wireless transceivers. Still more particularly, the present invention relates to a chopped intermediate frequency wireless receiver.
2. Description of Related Art
Unlike wireline communication environments, a wireless communication environment has to accommodate a large number of users sharing different parts of the frequency spectrum with very strong signals coexist adjacent to very weak signals. Hence, a wireless receiver should be able to select the signal of interest while rejecting all other signals. According to their respective architecture, wireless receivers can generally be classified under two categories, namely, homodyne receivers and heterodyne receivers.
With a homodyne receiver, the desired signal is initially selected by a bandselect filter and is subsequently amplified by a low-noise amplifier. The desired signal is then frequency translated by a mixer to DC before other baseband operations are performed on the desired signal. With a heterodyne receiver, the desired signal is sent through receiver components similar to those in the homodyne receiver with the exception that the desired signal is translated to an intermediate frequency (IF) when signal processing operations are performed.
For heterodyne wireless receivers, image rejection refers to the ability to select the desired signal from the image of the desired signal spaced away by twice the IF signal. Basically, a heterodyne wireless receiver should be able to select the desired signal from its image. Otherwise, the subsequent detector circuit within the heterodyne wireless receiver will not be able to distinguish between the desired signal and the image signal, and the output becomes the superposition of both signals. Accordingly, image rejection is one of the problems that are faced by designers of heterodyne wireless receivers.
Also, in many wireless receiver designs, all internally used oscillator frequencies are derived from a single high-accuracy reference oscillator, which can produce interference at fundamental, harmonic and sub-harmonic frequencies of the reference oscillator. The mixing of such interference frequencies with unwanted input signals is referred to as a spurious signal. Spurious signals are commonly found in wireless receivers. A wireless receiver may down convert a spurious signal that can interfere with the desired signal of interest, and as a result, the desired signal of interest can be corrupted.
The present disclosure provides a method and apparatus for alleviating the above-mentioned problems within a wireless receiver.